The present invention relates to a method for producing a novel green pigment composition that has clear hue, excellent light resistance and heat resistance, and that provides a green coloring material which causes no environmental problem since safety/sanitation related property is highly achieved and harmful substances are not generated at all in incineration.
Recently, problems concerning safety and sanitation due to some specific chemical substances and environmental pollutions by dioxin and the like have been becoming serious. Also in general public, there has been increasing concern about the safety to human bodies of some chemical substances and environmental problems. Under such conditions, promoting problem-solutions in industrial products from the viewpoint of their materials used has been advocated. Coloring materials such as pigments are not the exception that can be ignored. Particularly, under the recent circumstance, safety against human bodies and environments of the decomposed substances and by-products generated when the products are scrapped and burnt out has been regarded as the manufacturers"" responsibility. Further particularly, there is a tendency that halides, which may cause direct generation of PCB and dioxin in their incineration, are an excluder from the material components of products of routine use.
Presently, green color development in prints, colored substances and the like is typically effected by color mixing mainly using halogenated phthalocyanines typified by highly-halogenated phthalocyanine green, or by color mixing of phthalocyanine blue and disazo yellow. It is no exaggeration to say that a green pigment containing utterly no halogen atom in its molecular structure or in its pigmentary composition has not so far been found at all.
In the former case, due to halogen (chlorine) present in a large amount in the pigment""s molecular structure, there is a possibility of by-production or modification of the pigment substance into a chemical substance having high toxicity such as dioxin, in incinerating the prints or colored substances. In the latter case, although disazo yellow pigments such as, e.g., C. I. PIGMENT YELLOW 83, 12, 13, 14, 17, 55, and 87 have themselves sufficient heat resistance, if they are heated up to the temperature of 200xc2x0 C. or more in the molding process in their use as coloring materials in plastics, they are thermally decomposed. Therefore, the latter case is not preferable from safety/sanitation viewpoint and environmental viewpoint, also.
Because of such a circumstance, there have been trials to obtain a coloring material having the intended green hue and also having light resistance and heat resistance, by mixing a halogen-free phthalocyanine blue pigment and a halogen-free yellow high-grade pigment and intensely dispersing the mixture. However, by the conventional simple color mixing method, namely, mixing of a plurality of pigments and intense dispersion thereof, a coloring material having unclear hue can only be obtained.
In general, when a printing material or other substrate to be colored is colored by the application of a coloring material, different hues may be observed depending on the viewing angle. This phenomenon is called dichroism, and may be generated depending on the form and dispersion condition of the pigment particles used. Particularly, in a coated film formed by an ink or paint in which transparency and clearness of the film are important, the film may reflect some light having a specific wavelength at certain angle and the entire film portions reveal whitish, opaque, and hazy appearance, in some cases. Of phenomena of dichroism, such a phenomenon is particularly called xe2x80x9cfoggingxe2x80x9d. Such a hue change tends to appear particularly in a coloring material having low brightness, such as black, violet, blue, or green one. Among them, in a conventional green coloring material made by color mixing, the fogging phenomenon particularly tends to occur since color is controlled by mixing different pigment particles, and even if color control is tried to give the same hue as that of a halogenated phthalocyanine pigment, clearness of the resulting hue is extremely low. In a conventional green coloring material obtained by color mixing, because of difference in properties and conditions of respective pigments, each pigment has not been dispersed uniformly, consequently, hue has not been settled, and fogging and irregular color particularly have tend to occur.
Thus, a green pigment or a green pigment composition that maintains qualities required as a green coloring material, such as clear hue, good weather resistance and heat resistance, and that is satisfactory at the same time in the points of safety/sanitation related and environmental pollution problems above-mentioned, has not been found yet in the present state of the art.
The present inventors have intensively studied pigment selections, pigment qualities, particularly pigmentation processes, to overcome the above-mentioned present state, resultantly leading to completion of the present invention.
The present invention is a method for preparing a green pigment composition, the method comprising subjecting a halogen-free blue pigment material and a halogen-free yellow pigment material to an atomizing process in mixture. From a vehicle component and a green pigment composition prepared by the method, one can obtain pigment dispersion.
The atomizing process is preferably a co-kneading process conducted in the presence of a grinding agent. In this case, the co-kneading is desirably conducted in the presence of a glycol solvent. The grinding agent is preferably an inorganic salt.
Also, the atomizing process preferably comprises (a) dissolving the blue pigment material and yellow pigment material in a strong acid to obtain a solution and (b) injecting the solution into water to obtain a re-deposited substance. The strong acid may be, for instance, sulfuric acid, trifluoroacetic acid, polyphosphoric acid, or chlorosulfonic acid.
In the method for preparing a green pigment composition according to the invention, the ratio of the blue pigment material to the yellow pigment material is preferably from 90:10 to 40:60 by weight. In the preparation method, the blue pigment material may be at least one selected from the group consisting of phthalocyanine-type, threne-type, and indigo-type blue pigments. Also in the present method, the yellow pigment material may be at least one selected from the group consisting of azo-type, benzimidazolone-type, isoindoline-type, flavanthrone-type, anthrapyrimidine-type, anthraquinone-type, quinolinoquinolone-type, fluoroflavine-type, and fluorovine-type yellow pigments. It is desirable that the yellow pigment material is at least one pigment material selected from the group consisting of quinoloquinolone, fluoflavine, and fluorovine.
Pigment dispersion is a fine particle dispersion system in which each fine-size primary particle is in itself an assembly of crystallites of pigment molecules and in turn each pigment aggregate dispersed is one made of a plurality of such primary particles. The present inventors have doubted that by conventional pigment dispersion methods it might be difficult to attain a uniformly dispersed pigment system when considering the circumstance confronted, a system composed of fine particles and where strong interfacial effect is present therefore, particularly to make fine pigment particles from different production origins to mutually contact or access at their interfacial level. The present inventors now presume that in a green coloring material attained based on color mixing, the subject matter of the present invention, such a mutual access of different types of fine particles and uniform dispersion thereof have both been insufficient at a microscopic order and that the consequence has been extremely insufficient qualities in the conventional green coloring materials.
It can be understood that the present invention focuses on the unique interfacial environment provided by an atomizing process of pigment materials and effectively utilizes it in practice to solve the problems from their origins, problem origins that the conventional green coloring materials seem to have been confronted with so far, and as a consequence, to realize a green shade having qualities equal to or even superior than the qualities of other shades.
In general, an atomizing process of fine particles, pigment particles for instance, can be recognized as a process in which under various particle scales (primary particle, that is a collection of pigment molecule""s crystallites, and the aggregate, which is composed of a plurality of primary particles) each particle""s specific surface area is increased and the number of unstable molecules located at the surface portions is increased accordingly. Therefore in the process, the system is temporarily put under an unusual condition that is thermodynamically extremely unstable and has high energy. By subjecting both types of pigment particles to such an unstable system, which may be realized in an atomization process as above mentioned and where there is a nature existing to stabilize itself by mutual particle adhesion, mutual dispersion of both types of pigments at a microscopic level is propelled strongly. The present invention have achieved, consequently, a high-quality green shade on a color mixing basis, which has been the one strongly desired to date.